This invention relates to a damper device for an automatic folding chair for use in a theater or other public gathering place having a seat rotatably fitted to a fixed shaft of the chair, said device comprising a power unit for storing the resilient force generated in its spring means by rotary movement of the seat from a substantially upright standing position to a substantially horizontal ready-for-use position and a damper unit for damping the returning movement of the seat to the substantially upright position.
FIG. 6 of the accompanying drawings illustrates a known automatic folding mechanism of an automatic folding chair.
Here, an external end of a fixed shaft c is rigidly fitted to a seat supporting member a by means of grub screw b and a seat d is by turn rotatably fitted to said fixed shaft c as the latter is made to pass through a through bore disposed near the lower edge of the seat d. Said fixed shaft c is provided with a rod holder e projecting from the peripheral surface of the shaft for rotatably holding a bent end f' of a rod f, while a seat frame g is provided on an inner lateral surface with a spring-rod holder h projecting inward for holding the other end of said rod f so that the rod f may axially slide through a hole bored in the holder h. A spring j is arranged as seat folding means around the periphery of the rod f and between the spring-rod holder h and a spring holder i on the rod f.
A damper device for an automatic folding chair comprising a power unit and a damper unit of the type under consideration is also already known from Laid Open Japanese Utility Model No. 52-45784. The damper unit of a device according to the above identified document comprises a hollow cylinder for movably holding a shaft and airtightly containing damper liquid to produce a damping effect by the flow resistance of the liquid as it runs though an orifice (a small bore of a piston ring).
With an automatic folding mechanism as described above firstly, the spring j is compressed as the seat d is turned downward in the direction as indicated by arrow k from an upright position to a substantially horizontal ready-for-use position until the torque caused by the weight of the seat comes to exceed the power torque (spring power.times.rod length) of the spring j at a certain angle of rotation (approximately 80.degree. in most cases) of the seat d so that the seat d is kept to the horizontal position. When, on the other hand, the seat d is slightly turned upward by hand from the horizontal position, it will be automatically turned further upward by the power torque of the spring j until it reaches the upright position.
With such an arrangement, however, since the seat d is accelerated in its upward swinging movement, the chair is subjected to a large impact each time the seat d is turned upward to functionally damage the seat supporting member a and generate a noise. Additionally, since the fixed shaft c and the rod holder e and the seat frame g and the spring-rod holder h need to be rigidly bonded together by welding, manufacture of such folding chairs is inevitably accompanied by a problem of poor efficiency and high cost.
While an automatic folding chair as described above secondly comprises a damper unit to appropriately retard and decelerate the upward rotary movement of the seat from a ready-for-use position to an upright position, the seat also receives a flow resistance of the liquid contained in the cylinder also works when it is turned downward and therefore a considerable effort is required for moving the seat downward. Consequently, the seat cannot be quickly and lightly turned downward from an upright position to a ready-for-use horizontal position.
Besides, since the damper unit comprises a hollow cylinder containing liquid and a shaft running through the cylinder to make the unit rather bulky, it cannot be arranged in the vicinity of the peripheral surface of the rotary shaft that provides a pivot for the seat. The bulkiness of such a damper unit inevitably limits its practical applicability.
Therefore, in view of the drawbacks of the prior art, it is a first object of the present invention to provide a damper device for an automatic folding chair that enables its seat to be lightly pushed down to a ready-for-use position from an upright position without being subjected to a braking force and automatically return to the upright position once the user of the chair leaves the seat.
A second object of the present invention is to provide a damper device for an automatic folding chair having, in addition to the above capabilities, a feature of being applicable to a so-called self-stop type chair having a seat that automatically stops at a ready-for-use position once it is moved downward and a so-called non-stop type chair having a seat that automatically and slowly returns to an upright position once the user of the chair leaves the seat by simply modifying the extent of driving a adjuster screw fitted to its power unit.
A third object of the present invention is to provide a damper device for an automatic folding chair comprising a power unit and a damper unit and having, in addition to the above capability, a feature of being removably fitted to the rotary shaft of a chair by simply passing the shaft through corresponding bores of the device and securing the power unit to the rotary shaft by means of screws so that the damper device may become rotatable with the seat without bonding them together by welding and the overall cost of manufacturing such an automatic folding chair provided with a damper device may be significantly reduced.